1. Technical Field
The present invention relates to a transflective liquid crystal display panel. The invention further relates to an electronic apparatus that is provided with a transflective liquid crystal display panel.
2. Related Art
Recently, a transflective liquid crystal display panel has been developed actively. A transflective liquid crystal display panel has combined features of a transmissive liquid crystal display panel and a reflective liquid crystal display panel. A transflective liquid crystal display panel has a transmissive area (i.e., transmissive region) and a reflective area in each pixel area. The transmissive region has a pixel electrode. The reflective region has a pixel electrode and a reflector (i.e., reflecting plate). Under low light conditions, internal light is used for image display. That is, under such conditions, a backlight emits light, which passes through the transmissive area. On the other hand, in a well-lighted area, an image is displayed without turning the backlight ON. That is, under such conditions, external light that is reflected at the reflective area is used for image display.
In the technical field to which the present invention pertains, so-called vertical electric-field liquid crystal display panels are widely used as the mainstream electric-field mode thereof. In the configuration of a vertical electric-field liquid crystal display panel, an electrode(s) is formed on each of a pair of substrates. A few examples of such a vertical electric-field liquid crystal display panel are a TN (Twisted Nematic) liquid crystal display panel and a VA (Vertical Alignment) liquid crystal display panel. Although vertical electric-field liquid crystal display panels are predominantly used, horizontal electric-field liquid crystal display panels are also used in the related art. In the configuration of a horizontal electric-field liquid crystal display panel, electrodes are formed on only one of a pair of substrates. A few examples of such a horizontal electric-field liquid crystal display panel are an FFS (Fringe Field Switching) liquid crystal display panel and an IPS (In-Plane Switching) liquid crystal display panel, which are described in, for example, JP-A-2002-14363 and JP-A-2002-244158.
A transflective liquid crystal display panel has recently been developed also in the field of an FFS liquid crystal display device (refer to JP-A-2003-344837 and JP-A-2006-337625). With reference to FIGS. 14 and 15, an FFS transflective liquid crystal display panel of the related art is explained below. It should be noted that, in the accompanying drawings that will be mentioned in the following description of this specification, different scales are used for layers/members illustrated therein so that each of the layers/members has a size that is easily recognizable therein. Therefore, the dimensions of constituent elements that are shown in the accompanying drawings do not necessarily reflect, in proportion thereto, those that will be adopted in an actual implementation of the invention.
FIG. 14 is a plan view that schematically illustrates an example of the pixel configuration of an FFS transflective liquid crystal display panel of the related art; more specifically, FIG. 14 shows one pixel of an FFS transflective liquid crystal display panel of the related art. FIG. 15 is a sectional view taken along the line XV-XV of FIG. 14.
As shown in FIGS. 14 and 15, an FFS transflective liquid crystal display panel of the related art (50) is provided with an array substrate AR and a color filter substrate CF. The array substrate AR of the related-art FFS transflective liquid crystal display panel 50 has the following layer structure. A plurality of scanning lines 52 and a plurality of common lines 53 are formed on the surface of a first transparent substrate 51. The scanning line 52 and the common line 53 extend in parallel with each other. A plurality of signal lines 54 is formed over the array substrate AR. The plurality of signal lines 54 extends in a direction perpendicular to, or at least intersecting with, the plurality of scanning lines 52 and the plurality of common lines 53 when viewed in plan. A gate insulation film 55 covers the surface of the scanning line 52 and the common line 53. The gate insulation film 55 is made of a transparent insulation material. The signal line 54 is formed on the surface of the gate insulation film 55. A semiconductor layer 56 is formed on the surface of the gate insulation film 55. The semiconductor layer 56 is formed in such a manner that it overlaps, when viewed in plan, a portion of the scanning line 52 that functions as a gate electrode G with the gate insulation film 55 being sandwiched therebetween. A source electrode S extends from the signal line 54 so as to partially overlie the semiconductor layer 56. A drain electrode D also partially overlies the semiconductor layer 56. The gate electrode G, the source electrode S, and the drain electrode D make up a TFT (Thin Film Transistor). A protective insulation film 57 is formed over these lines, electrodes, and films (i.e., layers) explained above so as to cover the entire surface over the first transparent substrate 51.
An inter-bedded film, or, in other words, an interlayer film 58 covers the surface of the protective insulation film 57. The inter-bedded film 58 has surface roughness (which is not shown in the drawing) in the reflective area RA of each pixel. The surface of the inter-bedded film 58 is smooth for other area thereof. A reflecting plate 60 is formed at the reflective area RA of each pixel on the inter-bedded film 58. The reflecting plate 60 is made of aluminum or aluminum alloy. A lower electrode 61 is formed on the surface of the inter-bedded film 58 for each pixel. A part of the lower electrode 61 overlies the reflecting plate 60. The lower electrode 61 is made of a transparent electro-conductive material such as ITO (Indium Tin Oxide), IZO (Indium Zinc oxide), or the like. A contact hole 62 is formed through the protective insulation film 57 and the gate insulation film 55 so as to expose the surface of the common line 53. The lower electrode 61 is electrically connected to the common line 53 via the contact hole 62. A contact hole 63 is formed through the inter-bedded film 58 and the protective insulation film 57 so as to expose the surface of the drain electrode D of the TFT. The area at which the lower electrode 61 is formed includes the reflective area RA and a transmissive area TA. A partial area of the entire lower-electrode formation area at which the reflecting plate 60 is formed corresponds to the reflective area RA. The remaining area thereof at which the reflecting plate 60 is not formed corresponds to the transmissive area TA.
A capacitor insulation film 64 is formed on the surface of the lower electrode 61 and on/over the surface of the inter-bedded film 58. The capacitor insulation film 64 is made of a transparent insulation material such as silicon nitride or silicon oxide. The capacitor insulation film 64 covers the inner-wall surface of the contact hole 63 in such a manner that the drain electrode D of the TFT is exposed at the open bottom of the contact hole 63. An upper electrode 66 is formed on the surface of the capacitor insulation film 64 for each pixel. The upper electrode 66 is made of a transparent electro-conductive material such as ITO (Indium Tin Oxide), IZO (Indium zinc Oxide), or the like. The upper electrode 66 has a plurality of slits 65. The plurality of slits 65 formed in the upper electrode 66 extends in parallel with one another. Each end portion of each of these slits 65 is closed. The upper electrode 66 is electrically connected to the drain electrode D through the contact hole 63. An alignment film (i.e., orientation film) covers the surface of the upper electrode 66 and the plurality of slits 65 formed therein. Note that the alignment film is not illustrated in the drawing.
The color filter substrate CF of the related-art FFS transflective liquid crystal display panel 50 has the following layer structure. A light-shielding layer 68 and a color filter layer 69 are formed on the surface of a second transparent substrate 67. In addition, a planarizing film, that is, planarization film 72 is formed over (i.e., not directly on) the surface of the second transparent substrate 67. The planarizing film 72 covers both the surface of the light-shielding layer 68 and the surface of the color filter layer 69. A phase difference layer 71 is formed on the surface of the planarizing film 72 at an area corresponding to the reflective area RA. An alignment film that is not shown in the drawing is formed on the surfaces of the phase difference layer 71 and the planarizing film 72. The array substrate AR and the color filter substrate CF are set opposite to each other with a certain space left therebetween. Specifically, the array substrate AR and the color filter substrate CF are positioned opposite to each other in such a manner that the upper electrode 66 and the color filter layer 69 face each other. Then, liquid crystal 70 is injected into the space in such a manner that it is sealed between the array substrate AR and the color filter substrate CF. The related-art FFS transflective liquid crystal display panel 50 has the layer structure explained above.
When the related-art FFS transflective liquid crystal display panel 50 performs reflective display with the use of the reflective area RA, external light is reflected at the reflecting plate 60. Specifically, at the time of reflective image display, external light enters the panel 50 as an incident light beam and then gets reflected by the reflecting plate 60. Then, the reflected light goes out through the display surface thereof. This means that external light passes through the liquid crystal layer twice at the time of reflective image display. For the purpose of adjusting a phase difference that arises between the transmissive display in which an image is displayed as a result of optical transmission at the transmissive area TA and the reflective display in which an image is displayed as a result of optical reflection at the reflective area RA, the related-art FFS transflective liquid crystal display panel 50 is provided with a phase difference layer 71.
Specifically, the film thickness of the phase difference layer 71 is adjusted in such a manner that the retardation (i.e., phase difference) of the liquid crystal 70 at the reflective area RA equals to a quarter (¼) wavelength under the condition that the retardation of the liquid crystal 70 at the transmissive area TA equals to a half (½) wavelength. The retardation of the phase difference layer 71 is a half (½) wavelength. With the film-thickness adjustment explained above, the retardation for non-external light that passes through the transmissive area TA, which is a half wavelength, becomes equal to the retardation for external light that enters the panel 50 as an incident light beam and then gets reflected at the reflective area RA, which is also a half wavelength. Therefore, regardless of whether the transmissive area TA is used for image display (i.e., transmissive display) or the reflective area RA is used for image display (i.e., reflective display), it is possible to achieve excellent display performance.
The phase difference layer 71 of the related-art FFS transflective liquid crystal display panel 50 is typically formed by means of a photolithographic method, though not limited thereto. Therefore, the finished form of each of the side faces 71a of the phase difference layer 71 depends on, or, in other words, is influenced by, formation precision in the patterning process. For this reason, each of the finished side faces 71a of the phase difference layer 71 is not necessarily perpendicular to the formation surface thereof. That is, as illustrated in FIG. 15, each of the side faces 71a of the phase difference layer 71 could be inclined with respect to the formation surface thereof. In the following description, such a slanted structure of each of the side faces 71a of the phase difference layer 71 is referred to as “tapered” structure. The term “tapered” might have special connotation and/or meaning in this specification, the definition of which might differ from their customary meaning. When the side faces 71a of the phase difference layer 71 are tapered, a film thickness value measured at the side-face portion thereof deviates from a non-tapered film thickness value. As a result thereof, a phase difference value measured at the side-face portion thereof deviates from a non-tapered phase difference value. That is, if so tapered, it is not possible to obtain a desired phase difference value. Consequently, optical leakage occurs near the border between the transmissive area TA and the reflective area RA, which results in degradation in image display performance. Such degradation in image display performance is not unique to horizontal electric-field liquid crystal display panels. That is, the same problem arises for vertical electric-field liquid crystal display panels.